The present invention relates to a prosthetic implant device, and more particularly to such implants which include a polyethylene portion secured to a metal base. This invention is particularly suitable for use as a patellar prosthesis or a tibial prosthesis although it is not limited thereto.
Heretofore, various means have been used to provide secure attachment of a polyethylene implant portion to a metal base. U.S. Pat. No. 4,501,031 to McDaniel et al. discloses a metal base which includes notches about its peripheral edge to help secure a plastic bearing portion via molding to the base. U.S. Pat. No. 4,205,400 discloses a metal base which includes tapered holes therethrough which diverge away from the upper surface and a plastic bearing portion molded to the base and through the tapered holes to secure the plastic to the metal U.S. Pat. No. 3,506,982 includes a metal anchor 3 fixed into the plastic portion 4.
In addition, a metal-backed polyethylene patella known as the AMK Patella (described in a Depuy ad.RTM. in the July 1989 JBJS, p.68) utilizes a Porocoat porous coating on the upper surface of the metal base between the plastic and metal to lock the poly surface to the metal backing. This component also uses the Porocoat porous coating on the lower exposed surface of the base. The Porocoat coating consists of a plurality of small ball-shaped metallic particles as described by U.S. Pat. No. 3,855,638 to Pilliar.
The utilization of various porous materials to select exposed or outer surfaces of implants is well known to enhance to fixation of such outer surfaces to bone for bony ingrowth or, if a bone cement material is used for fixation, to more securely fix such outer surfaces to the bone cement. Other examples of various porous materials utilized on select outer surfaces of metal or poly implants are disclosed in U.S. Pat. Nos. 3,605,123 to Hahn; U.S. Pat. No. 3,906,550 to Rostoker et al.; U.S. Pat. No. 4,454,612 to McDaniel et al; U.S. Pat. No. 4,589,883 to Kenna; and 4,636,219 to Pratt et al. In addition, U.S. Pat. No. 4,479,271 to Bolesky et al. discloses a bottom base layer of porous fiber metal material, an intermediate metal reinforcing layer including at least one opening therein, and a top non-metal surface (such as polyethylene) which is molded to the base layer. The portion of the top polyethylene layer that is in contact with the base layer penetrates into the interstices of the porous metal material, hence securing the non-metal layer to the porous metal base layer.
U.S. Pat. No. 3,720,996 to Tschermak discloses a method of producing a tight connection between a synthetic body and a metal body which comprises inserting a porous sintered metal body into the synthetic body and then pressing them together so the plastic of the synthetic body penetrates the pores of the sintered metal body, and then connecting an additional metal body to the exposed portion of the porous sintered metal body.
U.S Pat. No. 4,007,494 to Sauer discloses a bone cap comprising a porous body adapted for bone ingrowth that is partially covered by a coating of non-porous biocompatible material such as polyethylene.
U.S. Pat. No. 4,213,816 to Morris discloses a method for bonding a porous coating of polymeric material to a rigid structural member that employs an intermediate substrate layer of material that is chemically compatible with the polymeric material, but has a lower melting temperature so as to flow into the pores of the polymeric material.
In addition, it is noted that it is known in the art of implants to separately manufacture a polyethylene portion and a metal portion and subsequently attach them by various mechanical means of locking. Often these separately manufactured poly and metal components enable the poly portion to be removably secured to the metal base. Examples of such devices are disclosed in U.S. Pat. Nos 4,795,468 to Hodorek et al. and U.S. Pat. No. 4,207,627 to Cloutier. However, it is not the intention of the present invention to address such removable attachment features, but rather to address the permanent interlock of a plastic portion to a metal portion.